Already mom to son Liam, 4, and daughter Stella, 2½, the reality star says her new addition will be joining an already boisterous brood.

"They are best friends but they are at that age where there's that love-hate relationship," Spelling told PEOPLE at the GLAAD Media Awards in Los Angeles recently. "[Liam] beats [Stella] up, and she just adores him."

But by nightfall, all is forgotten. "They want to sleep in the same room," Spelling said. "That's their new thing."